The invention relates to improvements in apparatus for movably supporting various types of commodities, such as beds (especially hospital beds) and the like. More particularly the invention relates to improvements in apparatus wherein the commodity which is to be moved or shifted is mounted on one or more casters and the casters are provided with brakes for their wheels as well as with blocking devices for their wheel frames. Still more particularly, the invention relates to improvements in apparatus which, in addition to one or more casters, comprise means for controlling the movements of the caster wheel or wheels with reference to the respective frame or frames (by controlling the application or disengagement of the brake or brakes), and for controlling rotation (swivelling) of the wheel frame or frames with reference to the carrier or carriers for the wheel frame or frames (by controlling the operation of the blocking device or devices).
German Auslegeschrift No. 1 505 786 of Haussels discloses an apparatus wherein the carrier for the wheel frame of each of several casters defines a cylinder chamber for a piston which is biased in one direction by a coil spring and is movable in the opposite direction in response to admission of compressed air. The piston rod of each piston is connected with a first lever which can block rotation of the wheel frame relative to its carrier. The first lever is articulately connected with a second lever which is mounted in the interior of the respective wheel frame and acts as a brake for the adjacent wheel. The wheel is braked, and the wheel frame is held against rotation relative to its carrier, when the spring in the carrier is free to maintain the piston and its piston rod in one end position. When the operator of the bed or another caster-mounted commodity wishes to disengage the brakes and to free the wheel frames for rotation relative to their carriers, the operator causes a control system to admit compressed air into the cylinders of the carriers so that the springs are caused to store energy and the pairs of levers are pivoted in directions to free to wheel frames as well as to disengage the brakes. In other words, the commodity can be rolled along the ground in any desired direction as long as the cylinders of all carriers are connected with the source of compressed air.
As a rule, a hospital bed is mounted on four casters, one for each leg of the bed, and the means for admitting compressed air to the carriers of the four casters is connected with the four carriers by discrete conduits for compressed air. The source of compressed air is a pump.
A drawback of the apparatus which is disclosed by Haussels is that the wheel frames of all four casters are free to swivel relative to the respective carriers when the wheels of all four casters are free to rotate relative to the respective frames, or that the wheels of all four casters are braked when the wheel frames of all four casters are blocked (i.e., when the frames cannot swivel with reference to the respective legs of the bed). In other words, it is not possible to block the wheel frames while the wheels are free to rotate or vice versa. This is due to the fact that the gaseous fluid which is used in the control system of Haussels cannot be admitted into or evacuated from the cylinders in the carriers of the casters in accurately metered quantities, i.e., compressed air is permitted to escape so that the springs can take over in order to maintain the blocking and braking means in operative positions, or compressed air is admitted at a pressure which suffices to move the pistons and their piston rods to positions in which the first levers cannot prevent swiveling of the wheel frames and the second levers cannot brake the respective wheels.
On the other hand, it is often desirable and advantageous to operate the casters in such a way that the wheel frames are blocked in a predetermined orientation while the wheels are free to rotate with reference to their frames.